Bird collisions on buildings is one of the leading causes of deaths to birds and there are some very obvious ways to mitigate this harm. The problem isn’t just skyscrapers, either, as most collisions happen in the first few floors, so even single-story glass sided buildings can be dangerous. Thankfully, there are solutions that work very well, as evidenced with this multi-year study on Portland’s Columbia Building in North PDX.
A Successful Monitoring and Mitigation Project to Address Bird Window Collisions at the City of Portland’s Columbia Building, 2015-2019
Avian window collisions kill an estimated 365-988 million birds each year in North America. This places collisions among the top three anthropogenic sources of mortality for wild bird populations, after habitat destruction and free roaming cats. A 2019 study indicates a nearly 30% decline in North American bird populations since 1970. Community science monitoring from 2009-2011 documented 69 species of warblers, thrushes, sparrows, hummingbirds, flycatchers, woodpeckers, and hawks that collided with buildings in Portland. Nationwide research shows that over half of all collisions occur at low rise commercial buildings, and that most collisions occur within the first 40-60 feet of a building where birds are most active, and vegetation is reflected in unmarked glass. In phase one, we initiated a yearlong effort to investigate the scope and scale of a known window collision issue at the City of Portland’s single-story glass-walled Columbia Building. We conducted twice weekly surveys and recorded collisions observed by building occupants. Phase one collision monitoring indicated a rate of 125-150 strikes per year and an estimated range of 65-115 mortalities per year. Collisions involved at least thirteen avian species and there was no clear seasonal pattern. In 2017, the building was retrofitted with a full-coverage window film featuring a horizontal line pattern. In phase two, we repeated our survey methods for another year, and documented a 94% reduction in window collisions on treated windows, with a post-retrofit estimated range of 7.5-9 strikes per year and an estimated range of 4-7 mortalities per year.
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